1. Field of the Invention
The present invention relates to a liquid crystal display element and more particularly to the electrode arrangement in such an element capable of improving the legibility or recognizability of a displayed pattern.
2. Description of the Prior Art
FIGS. 1a and 1b show the plan and sectional views of the main part of a typical prior art 7-segment type numeric liquid crystal display element. In the figures, numerals 1 and 2 designate opposite upper and lower substrates of transparent glass plates, numeral 3 designates seven transparent segment electrodes disposed on the inner surface of the upper substrate 1 to provide a form of numeral "8" as a whole which can selectively produce figures 0 to 9, and numeral 4 designates a transparent common electrode disposed on the inner surface of the lower substrate 2 opposite to the seven segment electrodes 3. The seven segment electrodes 3 and the one common electrode 4 opposite thereto constitute one pattern display section. A liquid crystal 5 is sandwiched between the upper and lower substrates 1 and 2 distanced by a predetermined interval and supported by a sealing material 6. In the illustration are omitted polarizers which may be disposed at the both sides of the paired substrates 1 and 2 respectively. A reflector used in the case of a reflection type display mode is also omitted.
With the thus constructed display element, a predetermined voltage is selectively applied between the segment and common electrodes 3 and 4 to change the optical characteristic of the liquid crystal at the superposing portion of these electrodes 3 and 4. This change of the optical characteristic is observed from the front side or upper substrate side of the display element. In FIG. 1a, dark patterns of figures "2" and "4" are shown to be displayed in a bright or light background. Such a display is made, for example, when crossed polarizers are arranged before and after the display element in the case where a 90.degree. twisted nematic liquid crystal is used.
Now, the display plane of the display element shown in FIG. 1a includes portions A of selected segment electrodes 3, portions B of non-selected segment electrodes 3, a region D having no segment electrode 3 within the display section, and a non-display area including regions C1 between the adjacent display sections and a region C2 outside of a set of the display sections. In operation, a selective voltage capable of exciting the liquid crystal is applied across the liquid crystal at the selected portions A while a non-selective voltage selected to be lower than the selective voltage is applied across the liquid crystal at the non-selected portions B. In a static or dynamic drive, it is possible to drive the display element without exciting the liquid crystal at the non-selected portions B, in a low multiplex driving range (for example, having a duty ratio up to 1/4). In a high multiplex driving fashion (for example, having a duty ratio smaller than 1/4), however, the applied non-selective voltage would cause the excitation of the liquid crystal at the portions B so that those portions have somewhat dark appearance, which renders the recognition of the display pattern of the dark portions A difficult. Namely, the display pattern of the portions is difficult to recognize since the area of the bright regions C1, C2 and D is large compared with that of the dark portions A and in addition to portions B become somewhat dark. This difficulty in recognition of the displayed pattern is due to the fact that one level must be recognized among three different and bright levels.
FIGS. 2a and 2b show the plan and sectional views of the main part of a typical prior art dot type alpha-numeric liquid crystal display element. In the figures, the same or like numerals and symbols are provided to the same or like components and portions as FIGS. 1a and 1b. In the example shown in FIG. 2a, one pattern display section is constructed by a matrix of 7.times.5 dots. Seven transparent x stripe electrodes 13 extend on the inner surface of the upper substrate 1 in the longitudinal direction thereof while a predetermined number (five per one display section) of transparent y stripe electrodes 14 extend on the inner surface of the lower substrate 2 in the transverse direction thereof. In FIG. 2a, each of the superposing or intersection portions of the x and y stripe electrodes 13 and 14 is shown to have a square form.
In the dot type display element shown in FIG. 2a, the recognizability of display pattern gets somewhat better since the area of a bright region D' having no insersection portions of the x and y stripe electrodes within the display section is smaller than that of the similar region D in the 7-segment type display element shown in FIG. 1a. However, the existence of bright regions C1' and C2' between the adjacent display sections and around the display section set still renders to recognition of the display pattern of the dark portions A' difficult.
The problem of the above-described difficulty in recognition of the displayed pattern holds also for the case where a bright pattern is displayed in a dark background.